1. Field of the Invention
The present invention relates to a turntable assembly for a video cassette recorder/reproducer and, more particularly, to a simple, accurate, and reliable turntable assembly for threading tape around a video scanner and across longitudinal magnetic heads and for engaging the tape to a capstan drive assembly.
2. Description of the Prior Art
Video recording tape is commonly supplied in a standard type of cassette to eliminate the problems associated with open reels and the threading of the tape into a video recorder/reproducer. When using a standard video cassette with a video recorder/reproducer, the cassette must be loaded into the system and the reels of the cassette must be mated to the reel drive system of the recorder/reproducer. Thereafter, the tape must be withdrawn from the cassette and threaded around the video scanner of the recorder/reproducer.
The video recorder/reproducers and associated mechanisms that have been developed heretofore have been intended for use in the recording and playing back of standard television type signals in either a home or commercial environment. In such systems, each tape is not used extensively and each frame of information recorded thereon is relatively unimportant since it is almost a duplicate of both the previous frame and the subsequent frame. Accordingly, the careful handling of the tape to maximize the life thereof and to preserve each and every frame of data recorded thereon has not been an important requirement. For similar reasons, accuracy, speed, and reliability of operation have been relatively unimportant considerations. It has also been relatively unimportant that a tape recorded on one machine be playable on another machine and vice versa since usually a single machine was used for recording and playing back information.
Furthermore, in prior systems, the tape travels at low speeds, typically 33/4 inches per second during playback and 45 inches per second during rewind. In addition, the rewinding occurs only after the tape has been unthreaded from the scanner so that the tape travels in only a single direction, for playing of same, when wrapped around the scanner. Furthermore, since the video scanner was typically the only recording/reproducing element in the system and such a scanner requires the tape to be wrapped around only half of the circumference thereof, typical turntables rotate through an angle of less than 360.degree.. It is therefore relatively simple to define the rotational starting and end points thereof.
On the other hand, the present turntable assembly is designed for a video recorder/reproducer intended for use in a document acquisition and retrieval system. This environment places a number of constraints on the video tape and the manner in which it is handled which cannot be satisfied with conventional tape handling mechanisms. For example, in such an environment, significant quantities of data, including address information, may be loaded on a single tape, representing a substantial investment in programming and information. Furthermore, the tape may be loaded and unloaded into the system many times each day. Therefore, in order to preserve each frame of data and to maximize the life of the tape, it becomes critical that the tape be protected and handled in a very gentle manner. Since a tape will typically be recorded in one machine and played back in another machine, it is important that the mechanism that handles the tape does so accurately and reliably so that the tape does not sense any differences from one machine to another.
If a turntable assembly is to be usable in a document acquisition and retrieval system, the threading of the tape must occur rapidly so that the system may quickly go into a search mode. Prior turntable assemblies have been too slow in operation for this use. Still further, because of the environment, the recorder/reproducer may be positioned at any angle, no necessarily horizontal, requiring the turntable assembly to control the tape track in any angular orientation. Accordingly, it is desirable that the turntable assembly not be subject to the influence of gravity, but be able to operate in any position.
The turntable assembly which helically threads the tape around the video scanner must handle the tape in a manner which minimizes the stresses placed thereon. The turntable must insure proper seating of the tape in the guide flange in the surface of the scanner and minimize unsupported tape lengths. Such turntable should have rollers and other guide elements rigidly connected thereto to increase reliability. The turntable must not only be capable of threading the tape around the video scanner, it also must be capable of threading the tape across longitudinal magnetic heads for recording and sensing address information. To achieve this, the turntable should be capable of rotating through an angle greater than 360.degree..
Still further, in a document acquisition and retrieval system, the tape travels in two directions, during a search mode, at speeds in excess of 400 inches per second and the tape accelerates to such speeds in approximately one second. The system must be capable of so operating with the tape threaded around the video scanner and the longitudinal heads for detecting the address information during the search mode.
Once the turntable assembly has threaded the tape around the video scanner and threaded the tape past the longitudinal heads, means must be provided to activate a pinch roller assembly for holding the tape against a capstan drive shaft. Such mechanism should be simple and direct in operation so as to insure reliability in use. A turntable assembly for a video cassette recorder/reproducer incorporating a mechanism which handles tape in a manner which meets the above requirements has been unavailable heretofore.